ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 538 (2005) 265–280
www.elsevier.com/locate/nima
Design and test of a prototype silicon detector module for
ATLAS Semiconductor Tracker endcaps
A.G. Clarka, M. Donegaa, M. D’Onofrioa, D. Ferrerea, R. Fortinb, J.E. Garciac,
S. Gonzalezc, C. Hirta, Y. Ikegamid, H. Kaganb, T. Kohrikid, T. Kondod,
S. Lindsaye, A. Macphersonb, M. Mangin-Brineta, B. Mikuleca, G.F. Moorheade,
T. Niinikoskib, H. Perneggerb,, E. Perrina, S. Roeb, G.N. Taylore, S. Teradad,
Y. Unnod, M. Vosc, R. Wallnya, M. Webera
a
Département de Physique Nucléaire et Corpusculaire, Université de Genève, CH-1121 Geneva 4, Switzerland
b
Department of Physics, CERN, CH-1211 Geneva 23, Switzerland
c
IFIC,CSIC-University of Valencia, ES-48071 Valencia, Spain
d
KEK, High Energy Accelerator Research Organisation, Tsukuba, Japan
e
School of Physics, University of Melbourne, Parkville, 3010 Victoria, Australia
Received 22 July 2004; received in revised form 2 September 2004; accepted 6 September 2004
Available online 1 October 2004
Abstract
The ATLAS Semiconductor Tracker (SCT) will be a central part of the tracking system of the ATLAS experiment.
The SCT consists of four concentric barrels of silicon detectors as well as two silicon endcap detectors formed by nine
disks each. The layout of the forward silicon detector module presented in this paper is based on the approved layout of
the silicon detectors of the SCT, their geometry and arrangement in disks, but uses otherwise components identical to
the barrel modules of the SCT. The module layout is optimized for excellent thermal management and electrical
performance, while keeping the assembly simple and adequate for a large scale module production. This paper
summarizes the design and layout of the module and present results of a limited prototype production, which has been
extensively tested in the laboratory and testbeam. The module design was not finally adopted for series production
because a dedicated forward hybrid layout was pursued.
r 2004 Elsevier B.V. All rights reserved.
PACS: 85.40. Ry; 29.40. Gx; 29.40. Wk
Keywords: Semicondutor radiation detector; Silicon strip detector; LHC; ATLAS experiment; Radiation hardness; Thermal
management; VLSI readout
Corresponding author. Fax: +41 2276 77150.
E-mail address: heinz.pernegger@cern.ch (H. Pernegger).
0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.nima.2004.09.001
, ARTICLE IN PRESS
266 A.G. Clark et al. / Nuclear Instruments and Methods in Physics Research A 538 (2005) 265–280
1. Introduction One of the main technical challenges at LHC is
the high radiation environment, with an expected
The ATLAS [1] Semiconductor Tracker (SCT) fluence equivalent to 2 1014 1 MeV neutrons/cm2
is part of the ATLAS Inner Detector system [2], in the case of the inner SCT layer for 10 years of
which provides charged particle tracking in the operation. It is therefore crucial to demonstrate
center of the ATLAS experiment. The Inner the radiation hardness of electronics and detectors
Detector system (ID) consists of a hybrid-pixel as well as the overall module. To limit anti-
detector in its center, followed by the SCT silicon annealing, which results from radiation damage to
strip detector and a gas straw-tube transition the bulk of the silicon sensors, the SCT will
radiation detector surrounding the SCT. A typical operate at an ambient temperature of 7 C: To
track will generate three hit points in the pixel guarantee a stable and sufficiently cold operation
detector, traverse eight silicon strip detectors (to of the detector for its entire lifetime, the modules
give four space points) and 36 straw tubes. The must have excellent thermal properties.
goal of the detector is to provide The large system size, 4088 detector SCT
modules with a total of 61 m2 silicon and 6.3
million readout channels, its very restrictive access
a hermetic coverage in a pseudo-rapidity range
and the expected lifetime of 10 years poses
of jZjo2:5;
additional challenges for component and system
an impact parameter resolution for high pT
reliability. An overview of the SCT system and
tracks of better than 11 mm in r f and 100 mm
integration considerations can be found in Ref. [3].
in z;
a momentum resolution for isolated leptons of
DpT =pT 0.4pT (TeV) (the ID is located in a 2 T
2. Module layout and performance requirements
axial magnetic field);
a low component mass to ensure a good tracker
The SCT consists of four concentric barrels at
and electromagnetic calorimeter performance.
radii of 299, 371, 443 and 514 mm with a length of
1.53 m, and two endcap sections of nine disks each.
In addition to these performance requirements, A schematic layout of the active detector part is
the SCT has to cope with the environment in a shown in Fig. 1, where each ‘‘box’’ represents one
high luminosity LHC experiment. The readout detector module. The SCT is based on five
electronics must be fast (p25 ns shaping time), different module types: one barrel module and
have low intrinsic noise and provide efficient signal four different forward module types, whose
processing. These electronics tasks have to be detector shapes vary with their different mounting
performed with minimal input power, typically radii. The SCT requires 2112 barrel modules and
7 W total per SCT detector module (4.5 mW/ 1976 forward modules. On the forward disks, the
channel) in a radiation hard layout. modules are arranged in concentric rings around
Fig. 1. Schematic layout of the ATLAS Semiconductor Tracker.
, ARTICLE IN PRESS
A.G. Clark et al. / Nuclear Instruments and Methods in Physics Research A 538 (2005) 265–280 267
the beam axis at three different radii. To achieve a geometry (six 128-channel chips per side), which
hermetic coverage across the disk, the forward are mounted on Kapton hybrids with four copper
module and silicon detector geometry varies for conductor layers. The Kapton hybrid is laminated
the three radii. Modules in the three rings are to carbon–carbon support substrates, which pro-
denoted as forward ‘‘inner’’, ‘‘middle’’ and ‘‘out- vide mechanical support and remove the heat
er’’ module. dissipated by the chips (approximately 7 W per
Each middle and outer module is based on four module).
single sided silicon strip detectors, where two on The ABCD3T readout chip is produced in the
each side are daisy-chained to give 12 cm long radiation hard DMILL process [5]. The input is
strips. The detector pairs are then glued back-to- based on a bipolar analog stage with preamplifier
back at a stereo-angle of 40 mrad to provide two- and shaper for each channel whose operation
dimensional position information in the detector currents can be controlled through DACs. For
plane. The inner module with 6 cm long strips has calibration and module tests, each channel is
only two sensors glued back to back. Each module equipped with a calibration capacitor which allows
has 768 active strips per side. charge injection into the preamplifier. The shaper
The layout of the forward silicon detector is followed by a comparator with adjustable
module presented in this paper is based on the threshold (one per chip) for sparsification. The
standard layout of the silicon detectors for the DC offset of each channel can be adjusted with a
forward SCT, their geometry and positioning on 4-bit DAC in four selectable ranges to compensate
disks, but otherwise uses components similar to for channel-to-channel variations. The binary
the barrel modules. We refer to this particular output of the comparator is strobed into a 132-
module design as the ‘‘KB’’ module layout, which cell deep FIFO. Between the comparator and
implements the electronics and hybrid of the barrel pipeline each channel can be masked off in case it
module [4] in the forward geometry. The electro- is noisy. The back-end of the readout chip
nics hybrid of the barrel module has been fully incorporates a de-randomizing buffer and data
developed and shows adequate electrical and compression stage. The readout stage also has
thermal performance. It carries the full front-end built-in redundancy links that allow to by-pass a
readout electronics of the module. The develop- faulty chip without breaking the readout daisy-
ment of a fully functional hybrid, which performs chain. Details on the chip architecture and
to our stringent thermal and electrical require- performance can be found in Refs. [6,7]. Each
ments, is often complicated by the complexity and module is read out with its dedicated optical link
sensitivity of the readout electronics and is there- to the readout driver in the counting room. The
fore a major technical challenge, which can result opto-fibre link to each module provides clock,
in numerous time consuming prototyping cycles. configuration, trigger and data readout for each
For those reasons it was deemed advantageous to module. Electronics required for the optical read-
study a module layout that is based on the forward out and control are implemented on a separate
module and silicon detector geometry but using Kapton tape. Each module is powered by its own
the electronic hybrid of the barrel modules. A independent power supply.
functional design of this kind provided the SCT
with a viable back-up layout in case unexpected 2.2. Silicon detectors
problems would have been encountered during the
prototyping of a dedicated forward hybrid. The SCT detectors are AC-coupled, single sided
strip detectors based on pþ strip implants in an n-
2.1. Readout electronics type silicon bulk [9]. The strip pitch on forward
silicon detectors varies between 70 and 90 mm as
The detector strips are connected at one end they feature a constant f-pitch of 161.5 mrad
through pitch adapters to the input of the (outer module) and 207 mrad (inner and middle
ABCD3T readout chip, in a so-called ‘‘end-tap’’ module). The sensor nominal thickness is 285 mm.
